1. Field of the Invention
The present invention relates to techniques for capping wells. More particularly, the present invention the relates to apparatus and methods whereby an interim Christmas tree can be installed onto the tubing spool of a wellhead so as to close the wellhead for a period of time. Additionally, the present invention relates to system and methods for closing a subsea well with a capping system.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
A typical subsea wellhead assembly has a high pressure wellhead housing supported in a lower pressure wellhead housing and secured to casing that extends into the well. One or more casing hangers land in the wellhead housing. The casing hanger is located at the upper end of a string of casing that extends into the well to a deeper depth. A string of tubing extends through the casing for production fluids. A Christmas or production tree mounts to the upper end of the wellhead housing for controlling the well fluid. The production tree is typically a large and heavy assembly, having a number of valves and controls mounted thereon.
One type of Christmas tree has a pair of bores extending through it. One of bores is the production bore and the other is a tubing annulus access bore. In this type of wellhead assembly, the tubing hanger lands in the wellhead housing. The tubing hanger has two passages through it. One passage is the production passage and the other passage is an annulus passage that communicates with the tubing annulus surrounding the tubing. Access to the tubing annulus is necessary to circulate fluids down the production tubing and up through the tubing annulus, or vice versa, to either kill the well or circulate out heavy fluid during completion.
After the tubing hanger is installed and before the drilling riser is removed for installation of the tree, plugs are temporarily placed in the passages of the tubing hanger. The tree has isolation tubes that stab into engagement with the passages in the tubing hanger when the tree lands on the wellhead housing. This type of tree is normally run on a completion riser that has two strings of conduit. In a dual string completion riser, one string extends from the production passage of the tree to the surface vessel, while the other extends from the tubing annulus passage in the tree to the surface vessel.
Unfortunately, the need for the production of oil and gas has created shortages in the availability of such Christmas trees. Often, the well cannot be completed until such time as the Christmas tree is available. In certain circumstances, the Christmas trees may not be available for over six months. In order to accommodate this problem, it is necessary for drillers to partially drill the well and then plug the well or cement the well so as to block the release of hydrocarbons from the well. The drilling rig can then be moved to another location.
Ultimately, when the Christmas tree is available for installation on the wellhead, the driller will move the drilling rig back to the location of the original hole, remove the plug, and begin to complete the drilling of the well. After the well is completed, the Christmas tree can be installed using the drilling risers.
Presently, the drilling rig can cost approximately one million dollars per day. As such, there is a great deal of waste of time and money during the time in which the Christmas tree is not available. The driller must rent the drilling rig in order to partially complete the well, wait for the Christmas tree, and then recall the drilling rig so as to complete the production process. Under certain circumstances, the driller may actually have the Christmas tree available, but must wait for the drilling rig to be available for the completion of the well. Ultimately, after the well is completed, the Christmas tree can be installed as needed.
Under current environmental regulations, plugs for the production tubing are not suitable. Under certain circumstances, leakages could occur where plugs are temporarily installed in the production tubing. Whenever these leaks would occur, an environmental disaster would result. If a simple cap were placed over the production tubing, then the pressures caused by a leaking plug, would prevent the cap from being removed. Ultimately, if the cap were removed, then the built-up or pressures and the leakage through the plug would escape into the marine environment. As such, a need has developed so as to provide a capping associated whereby the well can be appropriately capped in order to accommodate environmental considerations. This cap should be inexpensive and reusable.
In the past, various patents have issued relating to such Christmas trees and the plugs associated therewith. For example, U.S. Pat. No. 5,299,641, issued on Apr. 5, 1994 to Paulo et al., describes a Christmas tree for subsea production. The Christmas tree has a connector at a bottom thereof for the purposes of locking to the wellhead. A guide structure is provided having a central ring attached to the connector.
U.S. Pat. No. 7,596,996, issued on Oct. 6, 2009 to Zollo et al., provides a Christmas tree with an internally positioned flowmeter. This is a measurement device that has structure adapted to be removably coupled to the Christmas tree. A sleeve is operatively coupled to the structure. The flowmeter is positioned at least partially within the sleeve.
U.S. Patent Publication No. 2007/0034379, published on Feb. 15, 2007 to Fenton et al., provides a plug installation for deep water subsea wells. A plug retrieval and installation tool is used with a subsea well having a production tree, a tubing hanger, a passage that extends vertically through the tubing hanger, and the tree. A plug is located within a plug profile in the passage within the tubing hanger. The plug retrieval device has a housing and connector that is lowered on a lift line onto the upper end of the tree. An axially extendible stem in the housing is moved with hydraulic fluid controlled by an ROV into the production passage of the tubing hanger. An installation and retrieval member mounted to the stem engages the plug and pulls it upwardly in the passage while the stem is being moved upwardly and pushes the plug downward to install the plug while the stem is being moved downward.
U.S. Patent Publication No. 2009/0260829, published on Oct. 22, 2009 to D. J. Mathis, provides a subsea tree safety control system for limiting the probability of failure on demand of the tree. This subsea shut-in system serves to actuate a safety valve on the tree. The safety shut-in system includes a surface control station positioned above a water surface connected via an umbilical to a subsea control system positioned below the water surface to actuate the safety valve. The safety-in system is diagnostically tested without actuating the safety valve.
U.S. Patent Publication No. 20110036562, published on Feb. 17, 2011 to K. Braekke, discloses a well plug having a flexible expandable sealing and a metallic anchor that can be moved radially out or in by rotating a leadscrew in opposite directions. The well plug has a ball valve in a central longitudinal passage which is kept open whenever the leadscrew rotates. This increases the accuracy when setting the plug and reduces the risk of the plug moving uncontrolled in the well bore during setting or retrieval. The ball valve can be opened or closed by rotating a transmitting shaft within an angle of free motion before the leadscrew is pulled along in the rotation.
It is an object of the present invention to provide a capping system which serves as an interim Christmas tree until a proper Christmas tree is available.
It is another object of the present invention to provide a capping assembly that can be easily installed over the tubing spool associated with wellhead.
It is another object of the present invention to provide a capping system having an interior passageway whereby a plug within the tubing spool can be removed through the interior of the cap.
It is another object of the present invention to provide a capping assembly which allows for the monitoring and measuring of pressure on the interior thereof.
It is a further object of the present invention to provide a capping assembly which can be installed and removed without the need for drilling riser equipment.
It is still another object of the present invention to provide a capping assembly which allows a Christmas tree to ultimately be installed without the need for drilling riser equipment.
It is still another object of the present invention to provide a capping assembly which is easy to use, easy to install and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.